diff --git a/src/MetaTags/Entities/Tag.php b/src/MetaTags/Entities/Tag.php
index 24d60aa..550978d 100644
--- a/src/MetaTags/Entities/Tag.php
+++ b/src/MetaTags/Entities/Tag.php
@@ -82,6 +82,8 @@ protected function attributeElement(mixed $key, mixed $value): mixed
         if (!is_null($value)) {
             return $key . '="' . $value . '"';
         }
+
+        return null;
     }
 
     /**